Ah, i really dont wanna say this that possibly kills your enthusiasm. but i've tried almost all the anemones and ritteri really brought me a bunch of troubles:
1, rbta & gbta, 1 casualty outa many and they stayed put. but my occ found no way to accept it
2, sebae, no casualty outa 4. but my occ never gave em an f, u know what i mean
3, gig, no casualty outa 3, but they really ate fish. but i had to admit those eaten fish were unhealthy
4, ritteri, first one--self exile into some place in the tank and disappeared. sure died and dismembered
second, stayed put for a while then floated like a jellyfish and sure, sliced itself by huggin a powerhead. i saved the major piece but it didnt make it
third, this one did survived for almost 3 months. but my tank just underwent a major reaquascapin. now its mouth opened wider. no other bad signs so far tho